A common problem with electrical "extension cords" is that the ends of adjacent cords can be pulled apart easily, thus disconnecting the electric power. One technique for preventing this is to tie the two ends into a knot, but this tends to damage the cords and makes disassembly difficult.
Another technique for securing the ends of two cords together is shown in U.S. Pat. No. 3,316,523 (Trangmar) where an accessory is attached to each of the ends of the cords, and a leaf spring secures the accessories together.
Other devices for securing the ends of two cords together are shown in U.S. Pat. Nos. 3,097,034 (Jamrosy); 4,183,603 (Donarummo); and 4,784,612 (Ryan).